The present subject matter generally concerns a modular electronic assembly for use in a range of applications. Exemplary modules may correspond to functional modules for cell phones such as voltage-controlled oscillators (VCOs) and modules for use with Bluetooth brand technology, such as those developed and/or offered for sale by Bluetooth SIG, Inc. Corporation. More particularly the subject matter concerns modular electronic assemblies constructed using methods that produce a higher volumetric efficiency than previously possible. The present subject matter utilizes specialized assembly techniques to create a printed wiring board (PWB) that maximizes the available surface “real estate” for mounting other components while, at the same time, provides discrete components encased within internal areas of the PWB. An especially significant feature of the presently disclosed subject matter is the creation of a modular electronic assembly using techniques that produce modules with solder features containing significantly less lead (Pb).
The continually growing complexity of modern technical applications creates a constant need for improvement in the efficient use of available “real estate” on printed wiring boards. As electronic devices become smaller and, at the same time, more complex, there is an ongoing need to find ways to accommodate such conflicting desires. Recent efforts have been directed to the concept of moving passive elements off of valuable surface areas and into the printed wiring board itself. These efforts have resulted in multi-layered circuit boards where passive elements are built onto one or more internal layers of the PWB. This concept has been referred to as “embedded” or “integrated” passives.
Examples of known multi-layered printed circuit boards include U.S. Pat. No. 4,800,459 (Takagi et al); U.S. Pat. No. 5,866,952 (Wojnarowski et al); U.S. Pat. No. 6,038,133 (Nakatani et al); and U.S. Pat. No. 6,218,729 B1 (Zavrel, Jr. et al).
Problems have been discovered with such known multi-layer circuit board construction techniques based on a variety of causes. In prior printed circuit boards, passive elements have been either embedded or integrated into the core layers of the printed circuit boards. Embedded components, as disclosed in the Takagi et al (U.S. Pat. No. 4,800,459) patent noted above, require that cavities be provided within the various ceramic layers to accommodate chip-like electronic components. These cavities must be mechanically machined into the various layers and require precision placement of component holes especially when a component is larger than the thickness of one of the layers. This is a time-consuming process and can result in cracks that could render the substrate unusable.
Wojnarowski et al (U.S. Pat. No. 5,866,952) addresses further aspects of such cracking problems by teaching a circuit module construction technique wherein a material is molded around various electrical components. Electrical wiring connections are then provided to produce a circuit module. This technique addresses the cracking problem, but results in an unduly thick form factor for the module.
Another approach taken to address the surface “real estate” problem has been to integrate passive components directly into packaging substrates. Zavrel, Jr. et al (U.S. Pat. No. 6,218,729 B1) discloses one such technique wherein a multilayer substrate is composed of electrically conductive layers of interconnects separated by insulative layers of epoxy resin or ceramic and connected by vias. According to Zavrel's concept, passive components are integrated within the substrate at the definition stage during layout of the interconnections, but these components may be made from inferior quality materials. Often, it has been found that, upon completion of the printed circuit boards made with these techniques, final testing has shown that some components are defective. Such discoveries, after testing, can result in the entire circuit board being scrapped because of one faulty component.
Another problem with known printed circuit boards, and of presently growing concern, is the use of significant amounts of lead (Pb) in the solder used to attach passive, as well as active, elements to the printed circuit boards. It has become more desirable to minimize the use of lead.
Additional background references that concern electronic assembly modules and/or related aspects thereof include U.S. Pat. No. 5,373,627 (Grebe), U.S. Pat. No. 5,401,913 (Gerber et al), U.S. Pat. No. 5,497,033 (Fillion et al), and U.S. Pat. No. 5,888,627 (Nakatani). The disclosures of all the forgoing United States patents are hereby fully incorporated into this specification for all purposes by reference thereto.
While various aspects and alternative features are known in the field of electronics assemblies and other modular devices, no one design has emerged that generally addresses all of the issues as presented herein.